Neutral Earthing of Medium Voltage and Low Voltage Systems

This research paper discusses the different methods of neutral earthing for medium voltage and low voltage systems, including IT, TT, and TN networks. It also covers the benefits and drawbacks of solid-earthed neutral, unearthed neutral, solid neutral earthed system, resistance neutral earthing system, and resonant neutral earthing. The importance of safety, protection from overvoltage, and voltage stabilization is also emphasized. Course code, course name, and college/university are not mentioned.

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NEUTRAL EARTHING OF MEDIUM VOLTAGE AND LOW VOLTAGE SYSTEMS
A Research Paper on Earthing By
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Table of Contents
INTRODUCTION...........................................................................................................................................2
LOW-VOLTAGE SYSTEMS.............................................................................................................................4
Methods of Low-voltage System.............................................................................................................5
IT Networks.............................................................................................................................................5
TT Network..............................................................................................................................................6
TN Network.............................................................................................................................................7
MEDIUM-VOLTAGE SYSTEMS......................................................................................................................9
Methods of Medium-voltage System....................................................................................................10
Solid-earthed neutral.............................................................................................................................10
Unearthed neutral.................................................................................................................................10
Solid Neutral Earthed System................................................................................................................11
Resistance Neutral Earthing System......................................................................................................12
Importance of Medium-Voltage and Low-Voltage Systems......................................................................13
Safety for device, building, and human life...........................................................................................13
Protection from Overvoltage.................................................................................................................14
Stabilization of Voltages........................................................................................................................14
CONCLUSION.............................................................................................................................................14
BIBLIOGRAPHY...........................................................................................................................................15

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INTRODUCTION
A grounding system of the earthing system is a circuit which connects sections of the
electrical circuit with the ground, hence defining the electrical potential of the conductors with
respect to the conductive surface of the earth. The choice of the system is determined by the
compatibility of the electromagnetic and also the safety of the power system. Earthing system
specifically affects the distribution and magnitude of the current of a short circuit through the
system, and the impacts created by the people and equipment in the circuit proximity. In case of
a fault as a result of an electronic device connecting a conductor supply that is life to a
conductive surface exposed, any person coming into contact with it when connected electrically
to the earth will complete the circuit back to the supply conductor earthed and experience an
electric shock.
In the neutral earthing system, the neural of the transformer or rotating system or any
other system is connected to the ground. The neutral earthing system is a significant power
system design aspect of the system performance concerning protection, stability, or short circuit
is importantly affected by the neutral condition. A system of three phase can be operated in two
different ways namely with a neutral grounded and with ungrounded neutral. In the grounded
neutral system, the system’s neutral is connected to the ground. In this system, there is no
internal connection between the earth and the conductor (Bakshi, 2009).

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Figure 1: Grounded neutral (Bayliss, 2009)
Some of the benefits associated with the system above of grounded neutral include
improving service reliability, greater safety to equipment and operators, discharge of overvoltage
due to lightning, elimination of surge voltages due to arcing grounds, and also there is a
limitation of phase voltages to the line-to-ground voltages. Due to the issues related to the
systems of ungrounded neutral, there are grounded neutrals in the majority of the system of high
voltage. In the system with ungrounded neutral, the neutral is connected to the ground, hence this
system is always referred to as a free neutral system or isolated neutral system since the neutral
is isolated from the ground (Erkki, 2010).
Figure 2: Ungrounded system (Flurscheim, 2011)
LOW-VOLTAGE SYSTEMS
In this system of networks distribution, there is the distribution of electric power to the
numerous class of final consumers, the major anxiety for this system of earthing design
consumer safety who use the electrical equipment and their protection from electric shock. This
system of earthing together with devices of protection like residual current and fuses devices
should eventually ensure that an individual is not in contact with an object that is metal whose
relative potential is more than the safe threshold, normally set at approximately 50V. In case the

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earth is absence, equipment that requires a connection of earthing normally use the neutral of the
supply. Some use ground rods that are dedicated (Gouda, 2017).
Numerous appliances rated 110V have plugs that are polarized so as to maintain a
difference between neutral and live, however, using the neutral supply since the earthing of the
equipment can be troublesome. In case there is accidental energization of the fault path and the
connection supply has low impedance, the current of the fault will be huge such that the circuit
over the device of current protection like circuit breaker or fuse, will open to clear the ground
fault. In the case where the system if earthing does not supply a metallic conductor of low
impedance between the supply return and equipment enclosures, the fault current is minute, and
will not operate necessarily over the device of current protection (Heathcote, 2011).
Methods of Low-voltage System
There are three different earthing arrangement of the low-voltage system under the
International Standard IEC 60364. These include IT, TT, and TN networks. The initial letter
denoted the connection between equipment of power supply and earth. The equipment of power
supply can either be transformer or generator. Where T denotes the direct connection on an earth
point and I denotes that there is no connection with the earth, excluding possibly through a high
impedance. The second letter denotes the connection between the electronic device being
supplied and the earth. The letter N denotes a direct connection to the neutral at the beginning of
the installation which is coupled to the earth. The letter T denotes the direct connection of a point
with earth (Hewitson, 2012).

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IT Networks
In this type of network, the system of electrical distribution has no connection to the earth in any
way, or it possesses specifically a connection of high impedance. In this system, there is an
application of insulation monitoring device for impedance monitoring.
Figure 3: IT network (Internationale, 2010)
This system is characterized by the application of earth electrode at the site, high fault loop
impedance, cheap, continuity of operation in case of a fault, double fault overvoltage, low
electromagnetic interference, less safe, no risk of broken neutral, and low PE conductor cost.
TT Network
The term TT is an abbreviation of Terra-Terra, and in this system of earth, the earth connection
for protection of the users is issued by an earth local electrode, and also there is an extra
generator installed independently. There is an absence of earth wire between the earth electrode
and the generator installed. The impedance of the fault loop is higher, and the installation of the
TT earthing system should always have a GFCI (RCD) as its initial isolator unless the impedance
of the electrode is very low. The major shortcoming of this earthing system is a reduction in the
conducted interference from other connected devices of the users. This system has always been

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favoured for applications that are special such as in sites of telecommunication which benefit
from the earth that is free from interference (Jain, 2009).
This earthing system does not have dangers caused by broken neutral. In areas where there is the
overhead distribution of power and this earthing system is applied, earth conductors installation
is not at any risk of changing to live in case any conductor of overhead distribution is fractured
as a result of fallen branch or tree. This earthing system was not attractive for normal usage in
the pre-RCD era due to the trouble of arranging automatic disconnections that are reliable in case
short circuit caused by live-to-PE (Kiank, 2012).
Figure 4: TT network (Lehtonen, 2013)
The TT earthing system is characterized by high loop impedance, safe and reliable, low
electromagnetic interference, no risk of broken neutral, low PE conductor cost, need of earth
electrode at the site, and also high earth fault loop impedance.
TN Network
In this earthing system, a single point in the transformer or generator is coupled with the earth.
This point is normally the star point in the system of three-phase. The electrical equipment body
is coupled with the earth through the earth connection at the generator. The conductor that

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couples the uncovered metallic section the electrical installation of the earth are known as the
protective earth (PE). The conductor that conveys the return current in a system of single-phase,
or that connects the star point in a system of three-phase is known as neutral (N). The TN
earthing system can be categorized into TN-C-S, TN-C, and TN-S (Pabla, 2009).
TN-C-S: A part of this system uses PEN conductor combined, which is a particular section split
up into different lines of N and PE. The PEN conductor combined normally takes place between
the point of entry into the structure and the substation and separated in the head service.
Figure 5: TN-C-S (Prévé, 2013)
TN-C: This earthing system is made up of combined neutral (N) and protective earth (PE)
conductor all the way to the consuming equipment and transformer. A combined PEN conductor
satisfies the work of both N and PE conductor. This earthing system is characterized by low
earth loop impedance, high PE conductor cost, high risk of broken neutral, safe, and high
electromagnetic inference (Rajasekar, 2018).

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Figure 6: TN-C (Rajput, 2010)
TN-S: The Neutral (N) and PE are different conductors that are joined together specifically near
the source of power. This earthing system is the present standard for the majority of the electrical
systems in industrial and residential sectors. This earthing system is characterized by low earth
fault loop, high PE conductor cost, high risk of broken neutral, safest, and low electromagnetic
interference (Ravindranath, 2011).
Figure 7: TN-S (Sivanagaraju, 2012)
There are separate neutral and protective earth conductors to consuming device from the
transformers, which are not coupled together at any section after the point of distribution of the
building. This earthing system is characterized by low earth loop impedance, high PE conductor
cost, high risk of broken neutral, safe, and low electromagnetic inference (Strauss, 2011).

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MEDIUM-VOLTAGE SYSTEMS
This earthing system operates within the voltage range of 1kV to 72.5kV, which are far less
accessible to the overall public, the goal of this design of the earthing system is less on safety
and greatly on effects on the devices in the presence of short circuit, protection reliability, and
supply reliability. Specifically, the phase-to-ground short circuit magnitude is greatly affected by
the selection of the system of earthing since the current path is generally closed through the earth
(Tleis, 2010).
Methods of Medium-voltage System
There are five medium-voltage earthing methods, these include earthing transformer
system, resonant neutral earthing, resistance to neutral earthing, solid neutral earthing, and
unearthed neutral systems. These earthing systems are discussed below:
Solid-earthed neutral
In neutral directly earthed, the star point of the transformer is coupled directly to the ground. In
this system, a path of low impedance is supplied from the ground fault current to close,
consequently, their magnitudes are equivalent with the fault currents in three-phase. The voltages
are the phases unaffected remain at levels same to the ones of pre-fault since the neutral remains
at the potential near to the ground. This is the major reason why this earthing system is normally
applied in transmission networks involving high voltage where the cost of insulation is high
(Erkki, 2010).

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Unearthed neutral
This earthing system is also referred to as floating or isolated system. There is no direct coupling
on the ground and the star point. Therefore, a current of ground faults have no path to be closed,
hence have magnitudes that are negligible, practically, the fault current is not equal to zero since
the underground cables, particularly have an inherent capacitance towards the earth, which gives
a path of high impedance. Isolated neutral systems may proceed in their operation and supply
and supply power without interruption even in the incidence of a ground fault (Gouda, 2017). In
case of a fault, the potential of the other two phases reaches ∛ relative to the ground of the
normal voltage of operation, producing extra stress for the insulation. The failure of insulation
may impose extra ground faults in the system, but with much greater currents. In the distribution
network in the urban areas with numerous feeders underground, the capacitive current may attain
high current, imposing a great risk for the devices (Rajput, 2010).
Solid Neutral Earthed System
The solid neutral earth system is normally used in the applications of low voltage at 600V or
less. In this system, the neutral point is connected to the earth. This earthing system minimizes
the issue of transient overvoltages found on the pat provided and ungrounded system for the
current of a ground fault is in the range of 25% to 100% of the three-phase fault current system.
In case the transformer or generator reactance is too huge, the issue of transient overvoltages will
not be resolved. To maintain the safety and health of the system, the neutral of the transformer is
grounded and the grounding conductor must be extended from the source to the furthest point of
system so that a high fault current can flow hence making sure that fuses and circuit breakers
will quickly clear the fault and reduce the damage (Strauss, 2011).

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Figure 8: Solid Neutral Earthed System (Rajasekar, 2018)
The current magnitude depends on the fault resistance and fault location. The main advantage of
this system is that it involves low overvoltages, which makes the design of earthing common at
levels of high voltage. Some of the drawbacks of this system include high dangers for operators
due to high voltages created, o service continuity on the faulted feeder, and also maximum
disturbances and damage caused by high earth fault current. The solid neutral earthed system is
normally applied when there is low source short-circuit power, in three-phase neutral distribution
and in distributed neutral conductor (Strauss, 2011).
Resistance Neutral Earthing System
The resistance neutral; the earthing system is also known as earthing through a resistor and it is
where the neutral is connected to the earth through a single resistor. There are two categories of
the earthing system, these include low resistance earthing and high resistance earthing. These
two types of the resistance neutral earthing system are differentiated by the ground fault level
allowed to flow without any recognized standards for the earth fault current level which defines
these categories (Prévé, 2013).

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Figure 9: Resistance Neutral Earthing System (Flurscheim, 2011)
The current of the fault is limited to the selected value. Some of the reasons for limiting the
current by the use of resistor include to minimize the hazards of electric shock, to minimize the
mechanical stresses in the apparatus and circuits conveying fault current, to minimize the melting
and burning effects of electrical devices faulted. The low resistance value normally uses levels of
ground fault current between 10A and 3000A while the high resistance value normally uses the
level of ground fault current of less than 10A (Gouda, 2017).
The comparison of the various methods of medium-voltage neutral earthing systems is shown in
the table below:
Figure 9: Comparison of methods of the medium-voltage system (Bakshi, 2009)

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Importance of Medium-Voltage and Low-Voltage Systems
Safety for device, building, and human life
These systems protect the operators from death caused by electric shock by providing an
alternative path for the flow of fault current so that it does not endanger the human beings. The
appliances, machinery, and buildings which are under conditions of fault can also be protected,
from the excessive flow of current in case of faults. These systems also ensure that the all the
conductive parts exposed do not reach a critical potential by providing an alternative path for the
flow of fault current so that is the devices and operators are not affected (Erkki, 2010).
These earthing systems also provide a safe path for dissipation of short circuit and
lightning current. In case of short circuit, the fault current is channelled to the ground to protect
the equipment being used and also the operator. These systems also provide a stable platform for
sensitive electronic devices operation through maintaining the voltage at any section of the
electrical system at a specific value so as to prevent excessive voltage or overcurrent on the
equipment or appliances (Ravindranath, 2011).
Protection from Overvoltage
Unintentional contacts with higher voltage lines, line surges, or lightning can result in hazardous
high voltages to the systems of electrical distribution. Earthing ensures that there is a provision
of alternative paths through the electrical system to reduce the damages within the system.
These damages may be deaths and destruction of properties and buildings (Sivanagaraju, 2012).

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Stabilization of Voltages
Each transformer can be considered to be a separate source since there are numerous sources of
electricity. It would be very difficult to evaluate the relationship between each source of
electricity in case there was no common point of reference for entire sources of voltages (Rajput,
2010).
CONCLUSION
A grounding system of the earthing system is a circuit which connects sections of the
electrical circuit with the ground, hence defining the electrical potential of the conductors with
respect to the conductive surface of the earth. This research paper evaluates the importance of
neutral earthing of medium-voltage and low-voltage systems and also the various methods
involved in each system. In the low-voltage system, there is the distribution of electric power to
the numerous class of final consumers, the major anxiety for this system of earthing design
consumer safety who use the electrical equipment and their protection from electric shock. In the
medium-voltage earthing system, it operates within the voltage range of 1kV to 72.5kV, which
are far less accessible to the overall public, the goal of this design of the earthing system is less
on safety and greatly on effects on the devices in the presence of short circuit, protection
reliability, and supply reliability.

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BIBLIOGRAPHY
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Erkki, L., 2010. Electricity Distribution Network Design. New Zealand: Institution of Electrical Engineers.
Flurscheim, C., 2011. Power Circuit Breaker Theory and Design. Colorado: Institution of Electrical
Engineers.
Gouda, E.-S., 2017. Design Parameters of Electrical Network Grounding Systems. Perth: IGI Global.
Heathcote, M., 2011. J & P Transformer Book. Melbourne: Elsevier.
Hewitson, G., 2012. Practical Power Systems Protection. Sydney: Newnes.
Internationale, C., 2010. Electrical Installation Guide: According to IEC International Standards. Berlin:
Schneider Electric.
Jain, K., 2009. A Text Book of Design of Electrical Installations. Toledo: Firewall Media.
Kiank, H., 2012. Planning Guide for Power Distribution Plants: Design, Implementation and Operation of
Industrial Networks. New Zealand: John Wiley & Sons.
Lehtonen, M., 2013. Neutral Earthing and Power System Protection: Earthing Solutions and Protective
Relaying in Medium Voltage Distribution Networks. Toledo: ABB Transmit.
Pablo, A., 2009. Electric Power Distribution. London: Tata McGraw-Hill Education.
Prévé, C., 2013. Protection of Electrical Networks. New York: John Wiley & Sons.
Rajasekar, S., 2018. Practices in Power System Management in India. Michigan: Springer.
Rajput, R., 2010. Power System Engineering. Michigan: Firewall Media.
Ravindranath, B., 2011. Power System Protection and Switchgear. New Zealand: New Age International.
Sivanagaraju, S., 2012. Electric Power Transmission and Distribution. Mumbai: Pearson Education India.
Strauss, C., 2011. Practical Power Distribution for Industry. New Zealand: Elsevier.
Tleis, N., 2010. Power Systems Modelling and Fault Analysis: Theory and Practice. Colorado: Elsevier.
Willheim, R., 2009. Neutral Grounding in High-voltage Transmission. Perth: Elsevier Publishing Company.